Process for obtaining a composite article



United States Patent US. Cl. 29-472.3 8 Claims ABSTRACT OF THE DISCLOSURE The instant disclosure teaches a process for obtaining a composite article having a core of an iron base alloy clad with a dissimilar metal. The process is characterized by heating the core and rolling together the core and cladding at a speed of at least 100 feet per minute in one pass at a reduction between 35 and 75%, with the core and cladding coming together for the first time in the bite of the rolls.

This application is a divisional of US. patent application Ser. No. 465,156, filed June 18, 1965, now U.S. Patent 3,381,365 which in turn is a continuation-in-part of US. patent application Ser. No. 229,262, filed Oct. 2, 1962, now abandoned.

The present invention relates to composite metal articles. More particularly, the present invention resides in composite metal articles having an iron core and to the processes whereby said articles are obtained.

Composite articles having an iron core and a dissimilar cladding are highly desirable commercially due to the fact that the beneficial characteristics of the core and cladding materials may be obtained in one composite article. In a single alloy frequently many properties cannot be greatly modified by alloying or thermal treatments, for example, such properties as modulus of elasticity, color, density, and strength in combination with high thermal or electrical conductivity. However, by forming composites apparent properties of the cladding can be generated while retaining the bulk properties of the core material. In this manner one can often obtain greatly modified and highly desirable properties over the single alloy.

For example, iron has the advantage of high strength and cold formability. By forming iron composites one can retain these desirable properties While generating properties of the cladding, such as wear resistance, color, oxidation, conductivity, or tarnish resistance and fine finishing, i.e., surface quality.

Various uses to which composite iron articles may be put are as follows: heat exchangers, electrical hardware, builders hardware, utensils, automotive components, shipping containers and ornamental purposes.

However, the preparation of composite articles having an iron core presents numerous practical problems. It has been difficult to produce a satisfactory composite article having an iron core due to the tendency of the cladding material to form a layer of brittle, intermetallic compounds at the interface of the iron core and the cladding. This layer may form at moderate temperatures or at elevated temperatures. The brittle layer of intermetallic compounds which so forms may shatter readily on flexing of the composite material, thus clearly limiting the utility of the composite.

In addition, with composite materials having an iron "Ice core it is frequently difficult to obtain a well bonded composite which will Withstand normally expected use.

Iron presents further problems in the formation of composites due to the formation of both adherent and flaky oxides at moderate or elevated temperatures necessary for hot rolling. This oxidation will produce an interference oxide layer which inhibits bonding. This oxide layer frequently tends to break up on hot rolling but still can and often does cause severe problems.

One method of forming iron composites in order to overcome these difficulties is to form a partial bond by cold rolling followed by subsequent diffusion anneals. This is an expensive process and the diffusion anneals tend to degrade the properties of the composite.

Another method is to eliminate oxygen completely from the composite intersurface by, for example, evacuation and welding or treatment in enclosed, inert atmospheres. Another method is to provide bonding aids of one type or another. Both of these methods are expensive and undesirable alternatives, and often unsatisfactory.

Accordingly, it is a principal object of the present invention to provide new and improved composite articles having an iron core.

It is a further object of the present invention to provide convenient and expeditious processes whereby said composite articles are obtained.

It is a further object of the present invention to provide processes and articles as aforesaid whereby the articles are characterized by having high strengths, excellent physical properties and a wide variety of uses.

It is a still further object of the present invention to provide processes and articles as aforesaid which overcome the numerous limitations and disadvantages attendant upon the formation of conventional composite articles having an iron core.

Still further objects and advantages of the present invention will appear from the ensuing discussion.

In accordance with the present invention, it has now been found that the foregoing objects and advantages may be readily obtained. The process of the present invention readily overcomes the disadvantages of the art and achieves a simple and convenient process for obtaining a highly useful composite article clad on either one side or both sides and having a core of an iron base alloy clad with a dissimilar metal and preferably a material selected from the group consisting of a dissimilar iron base alloy, a copper base alloy, a lead base alloy, a silver base alloy, a nickel base alloy, a zinc base alloy, a chromium base alloy, a cobalt base alloy, a titanium base alloy, a tin base alloy and an aluminum base alloy. The process of the present invention comprises: (A) providing said core in plate form in a thickness less than /2 inch; (B) providing said cladding in plate form in a thickness less than inch; (C) heating said core to a temperature between 300 and 1,350 F.; (D) rolling together said core and cladding at a speed of at least 100 feet per minute in one pass at a reduction between 35 and with said core and cladding coming together for the first time in the bite of the rolls, said cladding contacting the roll prior to contacting said core, with the included angle between core and cladding upon entering the rolls being in excess of 5 degrees.

It is preferred to provide an angle between the cladding and core in excess of 10 upon entering the rolls in order to insure that the cladding and core will not come together earlier than in the bite of the rolls. Generally, the included angle between the core and cladding is between 5 and 22.

It has been found that poor results are obtained if there is no included angle between core and cladding upon entering the rolls or if pre-contact between core and cladding is had prior to the bite of the rolls.

In accordance with the present invention the cladding metal contacts the roll prior to contacting the core. On the front side of the rolls (entering side) the cladding and the rolls are travelling at different linear speeds; whereas, at the exit side they are going at the same speed due to the reduction in thickness of the composite. The difference in travelling speeds between the cladding and the rolls coupled with the pre-contact between the cladding and the rolls generates a shearing strain between the cladding and the rolls and introduces shearing at the bite of the rolls to the core-clad interface. This shearing strain at the core-clad interface results in turbulent flow of metal at the interface which causes more intimate bonding by increasing the interfacial linear surface of the composite by or more.

It has been found that the simple process delineated above achieves a highly advantageous composite article, with the interface between the core and cladding characterized by the absence of atomic interdiffusion between base metal and cladding, with said interface being further characterized by having at least 20% greater surface contact area than planar sheets.

The composite articles of the present invention are characterized by excellent physical properties, very high bond strengths and the absence of atomic interdiffusion between base metal and cladding, which interdilfusion may result in the formation of brittle compounds. The present invention achieves these surprising advantages by means of a simple and convenient process and without the use of expensive devices such as are frequently employed in the art.

In accordance with the present invention any iron base alloy may be employed as the core material, i.e., any alloy containing a major proportion of iron. Typical alloys which may be employed included but are not limited to the following: high purity iron, alloys of the ironcarbon family, iron-chromium family, iron-manganese family, iron-nickel family, and iron-nickel-chromium family, etc. Typical alloying substituents include but are not limited to the following: carbon, aluminum, titanium, silicon, lead, phosphorus, sulfur, chromium, nickel, zirconium and zinc.

The iron base alloy core material should be provided in plate form having a thickness less than V2 inch, i.e., the core material may be provided in strip, sheet or the like form.

It is preferred, but not required, in accordance with the present invention to mechanically roughen the bonding surfaces of both the core and the cladding materials in order to assure good surface contact at the bite of the rolls. For example, the surfaces may be wire brushed or abraded, etc.

The cladding material may be any of the cladding materials indicated hereinabove. The cladding may be, for example, any of the foregoing iron base alloys, providing that the cladding material is dissimilar to the core material. By dissimilar iron alloy or dissimilar metal, the present invention contemplates, inter alia, both an iron alloy having different alloying ingredients or the same alloy with different physical characteristics, e.g., stainless steel clad on mild steel.

In addition, any copper, lead, tin, nickel, zinc chromium, cobalt, silver, titanium, or aluminum alloy may preferably be employed as the cladding material. High purity copper, tin, lead, nickel, zinc, chromium, cobalt, titanium, silver or aluminum or base alloys of these materials may be readily employed.

Typical alloying substituents which may be employed include, but are not limited to, the following: with copper one may alloy zinc, tin, aluminum, phosphorus, iron and lead; with lead one may alloy tin, arsenic and cadmium; with tin one may alloy arsenic, cadmium, copper, lead and antimony; with nickel one may alloy chromium, iron, copper, titanium, aluminum, vanadium, tungsten, and cobalt; with zinc one may alloy copper, iron, alumimum and magnesium; with silver one may alloy copper and nickel; with aluminum one may alloy magnesium, copper, zinc, manganese, silicon, iron and chromium; and so forth.

The cladding material should be in plate form less inch in thickness, i.e., the cladding and the core material should be in wrought form, for example, coils of strip, sheet, etc. Therefore, the resultant composite has a thickness less than 0.60 inch where the iron is clad on two sides and less than 0.42 inch where it is clad on one side. The lowest gage materials, both core and cladding, which can be conveniently worked with, is on the order of 0.001 inch.

The starting materials, both core and cladding, can be in any temper or condition, hard or soft. Surface oxides are generally no handicap to the process of the present invention. This is quite surprising and is a significat advantage of the present invention since conventional processing must remove surface oxides prior to the formation of the composite. In fact, conventional processing frequently forms composites in special atmospheres so that one cannot form surface oxides prior to the formation of the composite. These special precautions are not required in the present invention.

It is, however, highly desirable to remove dirt or adhering lubricant from the surface of the metal prior to the process of the present invention in order to assure good contact between the core and the cladding materials. Any conventional cleaning processes may be readily employed, for example, the core and cladding materials may be passed through a soap or a detergent solution in accordance with conventional procedures. Examples of such cleaning procedures include the use of commercial alkaline cleaners and solvent cleaners, such as carbon tetrachloride and trichloroethylene.

It should be noted that it is a particular advantage of the present invention that it is unnecessary to utilize bonding aids, such as a thin coating of a dissimilar metal, in order to effect the strongly adherent coating of the present invention.

The core material is then heated to a temperature between 300 and 1,350 E, and preferably to a temperature in excess of 500 F. It is important to note that the cladding material is not heated but is left in the cold form.

The rolling step of the present invention is particularly critical. The core and cladding materials enter the rolls with the core material being provided at a temperature between 300 and 1,350" F. and preferably in excess of 500 F. The core and cladding enter the rolls at an angle so that they come together for the first time in the bite of the rolls. The materials are rolled at a high speed of at least feet per minute, in one pass, with a reduction between 35 and 75% and preferably between 50 and 70%. It is preferred that the core and cladding enter the rolls at an angle in excess of 10 and generally at an included angle of between 5 and 22 in order to assure that the core and cladding will not come together earlier than at the bite of the rolls and in order to put as much shear as possible at the interface. The shear at the interface enables the provision of at least 20% increased surface area than between the planar materials, i.e., the interface between the core and cladding is characterized by a wave-like formation with a significant increased interfacial contact area. It is further noted that the interfacial surface between the core and cladding is characterized by the absence of interatomic diffusion between the core and cladding material. For example, when a copper alloy cladding is used, there is substantially no diffusion of copper atoms into the iron core.

Further in accordance with the present invention the cladding metal contacts the roll before contacting the core metal. This is true whether the core is to be clad on one side or both sides.

Naturally, the present invention contemplates cladding the iron core on both sides with dissimilar metals on each side.

A further advantage of the present invention is that subsequent to the rolling operation the composites of the present invention do not require subsequent diffusion anneals, i.e., conventional processing frequently requires diffusion anneals to secure the bond between core and cladding. The fact that the present invention does not require diffusion anneals is particularly significant since diffusion anneals might and frequently do cause blisters or the like due to the long treatment times required and codififusion of gases to the interface between the core and cladding.

In fact, subsequent to the rolling operation no further operations whatever are required. The composites of the present invention are provided in commercial form ready to be used for the desired application. It may naturally be desirable to perform conventional subsequent operations for particular applications. For example, short thermal treatment for stress relief or the attainment of desired properties, e.g., a short heat treating anneal or aging treatment, a rolling operation for dimensional control, additional work hardening, and so forth.

The present invention will be more readily understandable from a consideration of the following illustra tive examples.

Example I In the following example the core material was a commercial grade iron alloy containing about 0.10% carbon in strip form having a gage of 0.040" and the cladding material was a copper base alloy containing about 89.0% copper and 0.04% lead, balance zinc at a gage of 0.010". All of the processing of these materials was conducted in air. Both the core and cladding were cleaned in an alkaline detergent solution, rinsed with warm water, dried with warm dry air and the surfaces of the core and cladding abraded with a rotating wire brush. After the cleaning and abrading steps the core material was placed in a furnace and heated to a temperature of 800 F. The core and cladding were then rolled immediately after the core exited from the furnace with the cladding material being rolled cold and with the core being clad on one side only. The speed of the rolls was 150 feet per minute, the materials were rolled in one pass at a reduction of 65% and the included angle between the core and the cladding was 18", with the core and cladding coming together for the first time in the bite of the rolls and with the cladding material contacting the roll prior to contacting the core.

The resultant composite was 0.018 inch thick, strongly bonded and the characteristics were as follows: (1) microscopic examination showed that there was no interatomic diffusion between the cladding and base material, (2) microscopic examination showed that there was at least 25% greater bonding area at the interface than with planar materials with the interface being characterized by a wave-like formation. The gage of the cladding after rolling was 00035-00004 inch, whereas the gage of the core was 0.014 to 0.0145 inch.

Example II The procedure of Example I was repeated except that the core was clad on both sides, i.e., with a second clad layer of the same cladding material of the same gage as in Example I. The included angle between claddings was 36 with the core bisecting this.

The potential assembly thickness before rolling was 0.060 inch and the resultant composite was 0.021 inch thick.

The characteristics and gage relationships of the composite were substantially as in Example I, except that the core was clad on both sides.

6 Example III Example I was repeated except that the total reduction was only 30%. Upon exit from the rolls the intended core and cladding came out as two separate materials exhibiting absolutely no bonding.

Example IV Example I was repeated except that the core and cladding materials came together prior to the bite of the rolls, thereby eliminating angulation into the rolls and eliminating precontact between the roll and cladding surfaces.

A single composite emerged from the rolls; however, the bond strength was quite weak and the core and cladding materials could be readily separated by hand.

Example V Example I was repeated except that the core was clad with two dissimilar copper base alloys, one on each side. One side was clad with 0.010 inch gage (upon entering the rolls) commercial gilding metal having about copper and 10% zinc, and the other side was clad with the same thickness commercial purity (99.9%) copper.

The characteristics of the resulting composites were substantially as in Example I.

Example VI Example I was repeated except that two separate composites were formed, both of which utilizing low melting claddings. Both cladding materials were 0.010 inch gage before entering the rolls and one was commercial soft solder containing 60% tin and 40% lead, while the other was a copper base alloy containing 3 /z4%% tin and 3 /24 /2% lead.

The procedure of Example I was repeated except that for both composites the core was heated to only 300 F.

The characteristics of both composites were substantially as in Example I.

Example VII Example I was repeated with the same core material in the same gage as in Example I and with a different cladding material. The cladding material was 0.010 inch gage (upon entering the rolls) commercial purity 1100 aluminum alloy.

The procedure in Example I was repeated except that the reduction was 60 to 65 The characteristics of the resultant composite were substantially as in Example I.

Example VIII Example I was repeated with the same core material in the same gage as in Example I and with a different cladding material. The cladding material was 0.020 inch gage (upon entering the rolls) cupro-nickel alloy, 92% copper, 8% nickel.

The procedure of Example I was repeated except that the reduction was 65-75%.

The characteristics of the resultant composite were substantially as in Example I.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A process for obtaining a composite article having a core selected from the group consisting of iron and iron base alloys clad with a dissimilar metal selected from the group consisting of aluminum and aluminum base alloys which comprises:

(A) providing said core in plate form in a thickness less than /2 inch;

(B) providing said cladding in plate form in a thickness less than inch;

(C) heating said core to a temperature between 300 and 1,350 E;

(D) rolling together said core and cladding at a speed of at least 100 feet per minute in one pass at a reduction between 35 and 75% with said core and cladding coming together for the first time in the bite of the rolls, said cladding contacting the roll prior to contacting the core, with the included angle between core and cladding upon entering the rolls being in excess of degrees, wherein said core and cladding are rolled together in direct metal-to-metal contacting relationship throughout the confronting surfaces thereof;

(E) wherein said processing is conducted under atmospheric conditions,

thereby forming an integrated composite article.

2. A process for obtaining a composite article having a core selected from the group consisting of iron and iron base alloys clad with a dissimilar metal selected from the group consisting of aluminum and aluminum base alloys which comprises:

(A) providing said core in plate form in a thickness less than /2 inch;

(B) providing said cladding in plate form in a thickness less than A inch;

(C) heating said core to a temperature between 300 and 1,350 F.;

(D) rolling together said core and cladding at a speed of at least 100 feet per minute in one pass at a reduction between 35 and 70%, with said core and cladding coming together for the first time in the bite of the rolls, said cladding contacting the roll prior to contacting the core, with the included angle between core and cladding upon entering the rolls being between 5 and 22 degrees, wherein said core and cladding are rolled together in direct metal-tometal contacting relationship throughout the confronting surfaces thereof;

(E) wherein said processing is conducted under atmospheric conditions, thereby forming an integrated composite article.

3. A process according to claim 2 wherein said included angle is in excess of 10.

4. A process according to claim 2 wherein said core is heated to a temperature in excess of 500 F.

5. A process according to claim 2 wherein said core and cladding are rolled together in one pass at a reduction between and 6. A process according to claim 2 wherein the surfaces of said core and cladding to be bonded are mechanically toughened prior to rolling.

7. A process according to claim 2 wherein said core is clad on both sides.

8. A process according to claim 2 wherein both said core and cladding are cleaned prior to rolling.

References Cited UNITED STATES PATENTS 1,792,377 2/1931 Jordan 29470 2,753,623 7/ 1956 Boessenkool 29497 2,782,498 2/1957 Mushovic 29497 2,879,587 3/ 1959 Mushovic 29497 X 2,908,073 10/1959 Dulin 29488 3,095,500 6/1963 Jost.

3,132,418 5/1964 Fulford 29497.5 X 3,165,829 1/1965 Wardlaw 29497.5 X 3,210,840 10/1965 Ulam 29488 3,269,004 8/1966 Smith 29471 3,352,005 11/1967 Avellone 29-497.5 X 3,300,837 1/1967 Fisher et a1.

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R. 

